Method of cold rolling and coiling strips



Nov. H, 1930. H. M. NAuGLE AL 1,781,123

I METHOD OF GOLD ROLLING AND CQILING STRIPS Original Filed Sept. 25, 1924 3 Sheets-Sheet, 1

l N I gnoentou 1501/. Mag/e H AJrw/we/M W Cltkznega v H. M. NAUGLE ET-AL METHOD OF com) ROLLING AND COILING STRIPS Nov. 1 1, 1930.

s Sh eeoS-Sheet, 2

' Original Filed Sept. 23, 1924 A. J Ybwnskmd Nov. 11, 1930. H. M. NAUGLE AL 1,731,123

METHOD OF COLD ROLLING AND COILING STRIPS Original Filed Sept. 25, 1924 3 Sheets-Sheet, 5

- Fig.4.

a: e .o 76 Z l o a l 50" m y a. O I, r- E I u c: I if I PERCENT LOAD 0N MOTOR 0 2'5 15 J I SPEED- LOAD CHARACTERISTIC CURVES l. DIFFERENTIALLY'WIOUND conpomw MOTOR 2. SHUNT WOUND MOTOR a. OUMULATIVELV wourm COMPOUND Mo'rbR Jena Patented Nov; 11, 1930 HARRY M. NAUGLE AND ARTHUR J. TOWNSEND, OF CANTON, OHIO, ASSIGNORS, BY

MESNE ASSIGNMENTS, TO THE AMERICAN ROLLING MILL COMPANY, OF MIDDLE- TOWN, OHIO, A CORPORATION OF OHIO METHOD OF COLD ROLLING AND COILING STRIPS Continuation of application Serial No. 789,302, filed September 23, 1924. This application filed April 28,

1927. Serial No. 187,186.

The invention relates to the reduction of strips of steel and the like to a finishing gauge by cold rolling and coiling the same; the object of the improvement is to impede 01 preclude the formation of imperfections in the strip and to remove such imperfections as may be formed therein; and this application is a continuation of our pending application filed September 23, 1924, Serial No. 7 39,302, for the same invention.

Each time a strip is reduced in thickness between cold rolls, the unavoidable variation in the pressure of the rolls from one side toward the other side of the strip, which may be caused by an unequal pressure adjustment of the ends of the rolls, or an inaccurate or uneven turning or wearing of the faces thereof, or an unequal heating of the body of the rolls, results in giving the strip a lateral camber, and sometimes a fullness in the middle portion which causes it to buckle between the edges thereof.

Furthermore, the elongation of a strip by the reducing action of successive mills, causes a looping of the strip between successive mills and between the last mill and the coiler, and a consequent bending or distortion of the strip.

And finally, the presence of the imperfections referred to, and especially, the presence of long loops in the strip, limits the amount of reduction which can be made by one of the mills, and requires mills to be operated at a comparatively low rate of speed, thus limiting the productive capacity of the apparatus.

The present improvement may be carried out by independently driving each successive tandem mill and the coiling drum at an increased peripheral speed from that-of the previous mill, and regulating the grip and the speed of same so that the strip is automatically stretched between successive mills and the coiler to give it a tension greater than the elastic limit of the metal, which will not'only elongate the strip and straighten the bends and buckles and the camber there may be therein; but will also prevent, to a certain extent, the formation of such defects by the cold roll reducing operations.

In this manner the strip is constantly kept in a tension greater than the elastic limit of the metal throughout all the operations, which not only prevents, either wholly or in part, the formation of the described defects, and precludes the accumulation of such defects as may be formed, but also acts to remove the same when they have been formed.

To this end, it. is necessary that each successive reducing mill and the coiler drum, shall grip and pull the strip with such a positive engagement as will constantly give the required tension greater than the elastic limit of the metal for the preventive and corrective operations upon the strip, so that the shorter sides and portions of the strip will be elongated to the full length of all other portions thereof, and will remain set at such full length against any elastic reaction to a shorterlength.

Such a result cannot be attained by the tension resulting from the engagement of finish,- ing cold rolls which do not have enough pressure to materially reduce the thickness.

steel strips in the finishing passes, may be as high as 90,000 pounds per square inch.

Nor can such a result be attained by a dif ferential tension control of the peripheral speed of successive mills, which merely equalizes the work of the rolls for reducing the thickness of a strip; for the reason that the tension required for such purpose is not sufli- .cient to stretch and straighten the strip for elongating the same to attain the results herein set forth.

Furthermore, such a result cannot be attained by merely pulling orstretching the strip with a tension approaching or even at about the elastic limit of. the metal, because the elastic limit of the metal in the strip must be fully exceeded to elongate any portion or all of the same, and the elastic tendency of the metal which has been elongated to con tract and return to its original condition must be entirely overcome, to accomplish the purpose of the present improvement.

And finally, the difierntialispeed control of each successive mill and the coiling drum must be automatically regulated so that while constantlymaintaining a tension exceeding the elastic limit of the metal, which is required for stretching, straightening and setting the structure of the strip, the tension will not exceed the ultimate strength of the metal and thereby strain'or sever the strip.

The object of the present invention may be attained by providmg each successive mill and the coiler drum with a cumulatively wound compound electric motor; and by increasing the. series winding as compared with the shunt wmding ordinarlly used in such a motor, so as to cause the motor to respond more readlly to slight variations in the load and to modify the'sp'eed in accordance therewith, thereby maintaining the necessary tension for straightening the strip by elongating the same without tearing it apart.

The invention is illustrated in the accompanyingdrawings, forming part hereof, in which Figure lis an outline plan view of a series of tandem cold rolling mills and a'coiling drum, showing the roll housing in section;

Fig. 2, an enlarged elevation section of two adjacent mills, each on line 22, Fig. .1;

Fig. 3, a similar section of the last mill of the series and an end view of the coiling drum;

Fig. 4, a conventional diagrammatic view of a cumulatively wound compound electric motor;

Fig. 5, a conventional section of a field core showing a one-half winding of the series coil;

Fig. 6, a similar view showing a one and one-half winding of a series coil; and

Fi 7, a diagrammatic view showing the speef-load characteristic curves of difierent types of motors.

Similar numerals refer to similar parts throughout the drawings.

The successive rolling mills 10,10, 10 and 10 of a tandem series and the coiling drum 11 at the end of the series, are driven by. .individual electric motors 11, 11, 11", 11 and 11; and for the purpose of the resent invention these motors are made 0 the cumulatively wound compound type, as diagrammatically shown in Fig. 4.

The speed load characteristic curve of such a motor is shown at 13 in Fig.7, as compared with the corresponding curve 14 of a shunt woundmotor and the corresponding curve 15 ofv a differentially wound compound motor; and as shown in Fig. 7, the percentage of speed decreases quite rapidly as the percentage of load increases in a cumulatively wound motor, thereby causing the speed thereof to respond very readily to differences in the load.

In order to increase the responsive action of such a motor, for the purpose of the present Fig. 6; which modification ofthe winding has proved very satisfactory in a standard of 250 H. P., 250 volt compound wound adjustable speed motor.

' The operation of tandem cold rolling mills for reducing the thickness of a steel strip in accordance with common practice, from an initial thickness of about one hundred and nine thousandths (.109) of an inch produced by hot rolling processes, to a final thickness of about thirty-twothousandths (.032) of an inch, may be described briefly as follows A first roughin operation may be carried out by a series 0 four stands of cold rolls, with or without a coiler at the delivery end thereof, by which the thickness of the strip is reduced from about .109 to about .062 of an inch; after which the strip .is preferably annealed, which may be done in-an ordinary annealing furnace.

A second roughing operation may then be carried out by a similarseries of cold rolls, which is preferably provided with a coiling device at the delivery end, as illustrated in Fig. 1, by which the thickness of the strip is reduced from about .O62'to about .036 of an 7 inch; it being understoodthat each stand of,

cold rolls performs its relative proportion of the reducing process, as the strip passes between the rolls thereof.

A levelling operation may. then be carried out by a single stand of cold rolls with or without a coiler, by which operation the thickness of the strip is reduced from about .036 to about 08501? an inch; after which the strip may be again annealed in an ordinary annealing furnace.

And finally, a finishing skin rolling operation may be carried out by a single stand of Ill cold rolls, which is preferably associated with i of the metal, from the delivery side of each stand of rolls.

The inherent characteristics of the motors when wound as described, causes each motor to automatically increase its speed when the strip tension load thereon is decreased, and vice versa; so that an elongating stretchin tension as aforesaid, is constantly maintaine upon the strip throughout its length from the delivery side of each stand of rolls to the next succeeding'stand of rolls or to the coiling drum, as the case may be.

The improved method of reducing a strip by one or more cold-rolling mills and a coiler, combined with motors as described, is illus trated in Figs. 2 and 3, wherein the course from one mill to another or to the coiler, of a strip or sheet stretched and elongated by constant tension is shown in full lines at 16 or 16; while the tortuous course from one mill to another or to the coiler, of a strip or sheet which is not stretched by tension, is shown in broken lines at 16 or 16 When an elongating stretching tension is constantly maintained upon the metal in a strip passing from one mill to another or to a coiler, the same not only serves to straighten any camber and to flatten any fullness there may be therein, but acts to avert more or less, the formation of such defects by thereducing pressure of the rolls.

And, it has been found, furthermore that the constant tension upon the strip not only enables the cold rolling and coiling apparatus to be operated at a much higher-speed, but permits a greater reduction to be made in the thickness of the strip by each pass between the rolls; thus greatly increasing the productive capacity of the apparatus, which can, moreover, 'be used to reduce strips of more than ordinary width, say up to some thirty or forty or more inches, when operated in a manner to carry out the improved method described herein.

W e claim The method of reducing the thicess of strips of steel and the like by tandem stands of rolls, which consists in constantly maintaining an elongating stretching tension greater than the elastic limit but less than the ultimate strength of the metal in the strip on both sides of each successive stand of rolls,

to straighten and set the structure of the strip; the pull on the strip extending between the successive stands of rolls being .caused by action of the succeeding stand of rolls upon the strip between it and the pro-- VlOllS stand of rolls.

HARRY M. NAUGLE. ARTHUR J. TOWNSEND. 

